STAT 2230 Lecture Notes - Lecture 11: Confidence Interval, Time Perception, Standard Deviation
23 Mar 2017
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Z( /sqrt(n)) = width of the confidence interval. Make z smaller by decreasing confidence level example: nicotine withdrawal and time perception population: all smokers in withdrawal. = mean time estimated when asked to count to 45. = standard deviation only know the population! Z( /sqrt(n)) confidence interval (ci) for (based on the sample) sample: n = 20. = 59. 3 s = 9. 8 this (standard deviation) is the next best thing to knowing. T( s /sqrt(n)) get our t value from a t-distribution instead of a. New: every t-distribution has a value called a degree of freedom" as the degree of freedom goes up, it looks more like a standard normal back to the time elapsed question. 95% ci degrees of freedom = n-1 (one less than the sample size) 20 smokers total, therefore 19 degrees of freedom. T( s /sqrt(n)) have everything but t at this point. R command: instead of qnorm() use qt(0. 975, 19)
